1. Field of the Invention
The present invention relates to devices and methods for marine propulsion and liquid pumping, and, more particularly, to such devices and methods for improving a performance of marine propulsion and pumping systems.
2. Description of Related Art
A cutlass bearing (common usage) is a special type of bearing used extensively in marine and industrial applications for bearings operating underwater or in other liquids. Cutlass bearings have no moving parts, and the bearing material is usually composed of a type of synthetic rubber and/or polymer, which supports the propeller shaft. Cutlass bearings are designed to utilize the lubricating properties of a hydraulic film of the surrounding water/fluid in which the bearing is operating. For this reason channels are designed within the bearing surface to promote the flow of liquids through the bearing, assuring proper lubrication while cooling the bearing and shaft surfaces at the same time.
A common problem in propeller-driven vessels is fouling of the propeller and shaft with lines, rope, netting, plastic bags, etc. When propeller shafts are fouled, often the fouling material is wound around the shaft in the section between the cutlass bearing and propeller hub. When this happens, the flow of water through the cutlass bearing is restricted and, in some cases, is cut off entirely. A vessel operator is sometimes made aware of a fouling condition because of vibration in the propulsion gear and diminished performance. If he is aware of the fouling, the operator will usually attempt to clear it by reversing the propulsion gear in an attempt to release the wound-up fouling, or, when that is not successful, someone may go overboard to clear the fouled propulsion gear. Even a small amount of fouling right next to the cutlass bearing will severely impede the flow of lubricating water because the cross-sectional area of the water channels in the bearing is relatively small. Small amounts of fouling around a propeller shaft, however, often goes unnoticed for extended periods. In this situation, the cutlass bearing suffers premature wear because of starvation of lubricating water. Furthermore, it is fairly common to have the aft ends of bearings and bearing housings physically damaged and abraded when fouling materials are tightly wrapped around the propeller shaft for an extended period.
Several devices have been designed and marketed for the purpose of preventing propeller and shaft fouling. They are generally based on rotary cutters that are attached to the shaft and act to cut the fouling materials as they begin to wrap around the shaft. Although some of these devices work well under the ideal conditions for which they were designed, they are not as effective in extreme conditions. These cutting devices generally require frequent repair and replacement in heavy use applications such as those experienced by vessels operating in the commercial sector. These devices also are not specifically designed to increase the flow of water through the cutlass bearing.
Therefore, it would be beneficial to provide a simple, robust, and dependable device and method of manufacture and use for substantially preventing fouling of propellers, shafts, and cutlass bearings in marine vehicles.